Many products today are conveniently packaged in and dispensed from pressurized "aerosol"-type containers. Aerosol packages typically are made up of (a) the product to be dispensed, (b) the propellant system, and (c) the container, valve, actuator and other accessories (the "hardware").
Conventional propellants used in aerosols include either liquified gases or compressed gases. The liquified gases fall into two chemical categories: (a) halocarbons (fluorocarbons, and chlorinated hydrocarbons); and (b) hydrocarbons (Kirk-Othmer, "Encyclopedia of Chemical Technology", Volume 3, Third Edition, (1978) page 586). An often used halocarbon is "fluorocarbon-12" such as "Freon 12.RTM., dichlorodifluoromethane. The hydrocarbon propellants used are liquified petroleum gases such as propane, butane and isobutane. The chief advantage of liquifiable propellants is that they maintain a constant pressure in the aerosol container until the contents are exhausted.
Compressed gas propellants typically used in aerosol packages include carbon dioxide (CO.sub.2), nitrous oxide (N.sub.2 O) and nitrogen (N.sub.2). Such gases are not in a liquid state in conventional aerosol containers. They are nontoxic, nonflammable, low in cost and very inert. However, the vapor pressure in containers which utilize these propellants drops as the container is depleted, possibly causing changes in the rate and characteristics of the spray.
The conventional "hardware" used in aerosol packages includes pressure containers such as steel or aluminum cans usually having a dome-shaped top provided with a circular opening finished to receive a valve. The valve is usually spring-loaded and is situated inside the can. The valve has an upper tube or "stem" extending outside of the dome top for connection to an actuator device which may also function to direct the flow of product from the stem. To allow dispensing of the product from the aerosol container while the container is in an upright position, the valve in many aerosol cans is connected at its lower end to a vertical, hollow "dip-tube". The dip-tube extends into the product and upon actuation of the valve, product is forced by the propellant up the dip-tube and out through the valve. Without the dip-tube, the aerosol can would dispense product only by inverting the container, a manuever which displaces the vapor normally surrounding the valve with product.
The ability to dispense product while the aerosol container is in an upright, vertical position is a very desirable practical advantage in the dispensing of many products. For example, aerosol dispensed, "single-component" polymeric foam systems used to seal joints and spaces in buildings and the like, can be difficult or awkward to use if the container is required to be held in an other than upright position. One such single-component foamable product presently in use and which can be dispensed in an upright position, comprises essentially a mixture of isocyanate, polyol, and liquid halocarbon propellant such as "Freon 12"(which also functions as a "blowing agent" to create a foam when the product is dispensed). The isocyanate and polyol react to form a "prepolymer" product in the container which is fluid when dispensed, but which cures soon thereafter into a non-fluid body of foam when in contact with atmospheric moisture. The product is packaged in an aerosol can of conventiona design having a valve, valve stem and dip-tube. Such product, while being conveniently dispensable in an upright position, sometimes is found to be unable to be dispensed by the user after packaging and delivery of the product and prior to its first use.